This invention relates to a treated metallic substrate useful for preparing lithographic printing plates photographically and the plates prepared thereby. More specifically, the invention relates to treated metallic substrates capable of being photographically imaged by the silver salt diffusion process to thereby produce lithographic printing plates, and the plates so produced.
In the silver salt diffusion transfer process, an imagewise exposed silver halide emulsion layer is positioned in intimate contact with a receptor element and developed in the presence of a silver halide solvent such that the unexposed silver halide diffuses into the receptor element where it is then developed to provide an image thereon. Development nuclei, contained on the receptor element, cause the diffusing silver halide to be reduced to metallic silver, thereby forming the image on the receptor element surface.
When a lithographic plate is the desired end product, a receptor element is utilized having a surface which is sufficiently hydrophilic so as to accept aqueous fountain solution preferentially to oleo ink. Common receptor elements in this instance include foils of amphoteric metals such as aluminum, zinc or copper. Subsequent to imaging these metallic receptors by the silver salt diffusion process, the silver image areas can typically be treated to render them oleophilic, i.e., receptive to oleo ink, so as to provide a lithographic plate.
The metallic receptor elements must present a surface capable of developing transferred silver halide to metallic silver. Typically, the foil surface can be nucleated by deposit thereon of conventional development nuclei, such as colloidal silver, colloidal gold, metal sulfides, e.g. nickel sulfide or other materials which either are nuclei for development by themselves or which provide such nuclei by interaction with the diffused silver halide during image development. Alternatively, as is taught in U.S. Pat. No. 3,186,842, an aluminum surface itself, without treatment thereof with development nuclei, can actively participate in silver image development by an electrolysis mechanism to thereby provide a lithographic plate.
However, one problem area common to presently available metallic lithographic plates imaged by silver salt diffusion transfer is that of sufficient adhesion of the silver image areas to the metallic foil surface so as to withstand the rigor of extended press runs.
In contrast with such prior art, a simple treatment of hydrophilic-surfaced foil with water soluble Group IV-B metal fluoride compounds has been found to provide a nucleated metal surface to which the silver image areas adhere to the extent that extended press runs are available.
Utilization of Group IV-B metal fluoride compounds in the preparation of metal lithographic plates is known in the art. For example, U.S. Pat. No. 3,440,050 discloses treating anodized aluminum sheets with a hot aqueous bath of such fluoride compounds preparatory to applying a lightsensitive, e.g. diazo, coating thereover. After imaging and development to remove unexposed diazo, a lithographic plate is produced.
Such materials have also been utilized in solutions in combination have hexavalent chromium to render aluminum surfaces highly resistant to corrosion without marring the surface thereof, as is taught in U.S. Pat. No. 2,825,697.
However, to my knowledge, no one has determined that by a simple treatment of hydrophilic-surfaced metallic foil with such fluoride compounds, the treated foil can provide a lithographic receptor element imageable by the silver salt diffusion process wherein the silver image has excellent adhesion to the metal so as to provide a lithographic plate capable of extended press runs.